Single-based high-pressure discharge lamps usually are metal halide discharge lamps. Lamps having higher power ratings, that is, in the order of from about 500 to 2500 watts, and relatively high color temperature, are used as light sources for film and television studio illumination. The discharge vessels of these lamps require a mount or holding structure which ensures stable retention of the discharge vessel within an outer bulb. Change in position of the axial alignment of the discharge vessel, for example due to vibration, shocks and the like, must be avoided. Such lamps are frequently associated with an optical system, where the position of the light source relative to the base is important.
Lamps of this type have a serious problem since, due to the high power rating, high temperatures result. Different thermal coefficients of expansion of the various components of the lamps cause difficulties.
German Patent Disclosure Document DE-OS 30 06 846 (to which, in the English language, Canadian 1 135 781 corresponds) shows a solution to such problems. Both ends of the discharge vessel are surrounded by a guide element in form of a metal collar, which is connected to a respective part of the holder of the discharge vessel. The discharge vessel is guided in an axial position, and thermal expansion thereof is possible only in axial direction. Lateral expansion or deflection, for example by impact or vibration, is avoided.
The system requires comparatively complex manufacturing steps and is difficult to make, since the mount or support frame structure is formed of a multiplicity of parts or elements.
The high-pressure discharge lamp of the referenced U.S. Pat. No. 4,734,612, Sasaki et al (to which European Patent Publication 0 209 345 corresponds) has a somewhat simpler mount structure. A single element support frame is used, and solely retained within the pinch seal of the outer bulb. Some additional support of the mount element is given by a partial cover thereof of glass, for example a glass tube, which in part is melt-sealed within the outer bulb.
The discharge vessel holder arrangement is suitable for lamps of relatively small dimensions, and for low power lamps, for example high-pressure discharge lamps having a power rating of up to about 100 watts. High-pressure discharge lamps of higher power rating, and particularly substantially high power rating by a factor of 10 or more, cannot use this construction. The holder arrangement is not sufficiently stable for discharge vessels of the size required to operate at the substantially higher power levels.
High-pressure discharge lamps with power ratings of from 500 to 2500 watts are commercially available. These lamps have a mount or support structure which utilizes a cross element extending orthogonally to the axis of the lamp, and welded to a current supply of the distal end or remote end of the discharge vessel. The remote end of the current supply is extended beyond the weld point and supported within the outer bulb, for example at the pump or exhaust tip, or in a bulged portion within the outer bulb. High-pressure discharge lamps of particularly high power rating, in the order of from 1200 to 2500 watts may, additionally, use holder rings or tension bows, welded to the distal current supply leads and to the cross element and engaged at the inner wall of the outer bulb, for example by a clamping or resilient connection.
Lamps of this type require expensive manufacturing steps, and attachment of the additional holder rings or clamping elements increases the manufacturing costs of the mount or support structure. Lamps without suitable holder rings or clamping elements do not have sufficient resistance to vibration or shock.